The specific aims of this proposal are to identify the formyl peptide receptor on alveolar macrophages and to determine its role (initiation, regulation, etc.) in the stimulation of O2- production by these cells. The formyl peptide receptor on the alveolar macrophage has thus far been poorly studied. However, since the macrophage has a significant role as a first line of host defense in the lung, the formyl peptide receptor (potential bacterial metabolite receptor) on the macrophage merits a thorough evaluation and characterization. To conduct the various aspects of this proposal, a number of radioactive and fluorescent derivatives of formyl peptides will be synthesized. With these, binding studies (kinetic, equilibrium and competitive) will be conducted to determine 1) if there are subpopulations of cells isolated by three techniques (density, affinity chromatography and cell sorter), 2) receptor cooperatively including receptors for other stimulators and 3) whether changes in membrane fluidity (anisotropy experiments) and receptor mobility are linked and what are the energetics of receptor binding. Some of the derivatives will be covalently bound to the receptor protein which will permit identification, isolation and measurement of chemical modification of the protein. Biophysical measurements (photobleaching, energy transfer and anisotropy) will be combined with visual techniques to determine what is the quality and quantity of receptor motion preceding and anteceding O2- production. Overall, these studies will permit a correlation to be made between the physical properties (i.e., binding, mobility and cooperativity) of the formyl peptide receptor (i.e., putative physiological bacterial metabolite receptor) and biological properties of the cell (i.e., O2- production and down regulation). If regulation of O2- production (possibly granular enzyme release and chemotaxis) is at the receptor level, then an understanding of this phenomenon would facilitate possible control of these processes. Where possible, extrapolation will be made to the human system.